It is normally quite straightforward to recognise that there is something wrong with your pet's eyes. In most diseases that affect the eye, the eye will look sore or there will be excessive discharge. If your pet has a reddened or runny eye, is blinking a lot or pawing at its face then an early trip to the vet is advisable.
Eye problems can be caused by a foreign body in the eye - often a grass seed or piece of dirt; a scratch on the eye caused by a cat's claw or running into a twig; or a simple eye infection. To work out what is wrong with the eye your vet will need to examine it carefully. Any foreign material in the eye can be removed and it is likely that your pet will need some eye drops or cream for a few days afterwards.
Blindness is not commonly recognised in pets and if your pet is only blind in one eye they may compensate well and show no signs. However if an animal has gone suddenly blind in both eyes this will be easy to recognise as they will be bumping into obstacles and may appear disorientated or frightened and be unwilling to move. Animals in which blindness has developed more slowly may adapt much better and often vision can be very poor without owners realising there is anything wrong with their pets.
If you suspect any problems with your pet's eye you should make an appointment with your vet. Sore eyes can deteriorate very rapidly and urgent attention may be required to prevent further or permanent damage to the eye.